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Angled chimneys & sloped flues: this article explains the hazards of angled or sloped masonry or metal chimneys and chimney flues.
Discussion includes code & safety issues with angled chimney flues - proper cutting of clay flue tiles for an angled flue; maximum angle for sloping chimney flues.
These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Angled and Offset Chimney Flues - Specifications & Concerns with Sloping Chimneys & Flues
This article series describes chimney defects and hazards that can be observed from on-roof access, including damage to a masonry chimney top, antennas mounted on chimneys, and angled chimney flue hazards.
Our photo at page top shows a chimney that was angled severely beginning at the attic floor - look there for cracks that may have opened, forming a fire and gas hazard.
Offset or angled chimney flues are found in both masonry and metal chimney installations.
Especially where multiple flues are routed inside of a single large masonry chimney or inside of a single wood-framed chimney chase, it should not be a surprise to discover that one or more of the appliances venting into one or more of the flues has to send its gases up at an angle to reach the final vertical section of flue in the chimney.
Look for these clues that may indicate angled chimney flues that deserve further inspection:
Large masonry chimney with two or more internal flues, serving one or more fireplaces.
Large chimney chases serving two or more metal flues with one or more fireplaces installed in the building.
View down a large masonry chimney from roof top that shows flues angling off to fireplaces or other building flues
Chimneys in attics that have been excessively corbelled or leaned to one side
Just as we reported that a clay tile lined chimney would be difficult to clean due to projecting concrete between vertically-stacked clay chimney tiles, clay tiles need to be cut properly when constructing an angled chimney such as the one shown in Carson Dunlop Associates [at REVIEWERS] sketch.
The sketches shown at left shows the concern with proper miter joints in a sloping masonry chimney flue.
[Click to enlarge any image]
Only the bottom design, showing that the clay chimney tile was cut on an angle, is correct.
The top two designs risk both cleaning difficulties and also water, smoke, soot,or creosote leaks into the chimney structure.
The next Carson Dunlop sketch at left shows that a masonry flue is limited to 30 deg. offset, or in some jurisdictions, 45 degrees of offset while a metal flue may, in some areas, be permitted to slope to 60 degrees of offset.
In sum, concerns about angled or sloping chimneys and chimney flues include:
Protruding or improperly cut clay flue tile liners that leak or that obstruct cleaning
Too-flat low slope chimney flues may accumulate ash, soot, creosote, leading to a blocked flue and requiring extra cleaning measures
Metal chimney flues also cannot be sloped too gently nor for too great a distance or draft and clogging problems occur.
A metal chimney might be permitted to run at angle of up to 60 deg. of slope in some jurisdictions.
See TRIPLE-WALL METAL FIREPLACE CHIMNEYS for additional sketches and details about angled or sloping metal chimneys and flues and for a fireplace metal chimney inspection checklist.
Support Rules for Sloped Chimneys & Elbows in Metal Chimneys & Flues
If elbows are used in the chimney the slope cannot be less than 30 degrees, and the sloping segment of the chimney above each elbow must be supported by straps or other means specified by the chimney manufacturer.
Question: can I slope the oil fired furnace flue pipe at 45 degrees? What about 30 degrees?
2018/02/11 John said:
I have an attached garage that I want to put a oil fired furnace in. I am curious if I’m allowed to put flue pipe at a 45 degree angle in attic space to get horizontal distance from house to the required 10 feet.
Illustration of a 30 degree chimney angle installation for an insulated metal chimney, adapted from Selkirk's installation instruction for the company's SuperVent 2100 cited below.
[Click to enlarge any image]
Reply: maximum number of 15° or 30° elbows and maximum non-vertical length for an insulated metal chimney indoors
We too found some sources warning that a 45° or 30° metal chimney might be out of compliance with UL 103 and may presented increased risk of chimney fire, particularly where soot or debris can accumulate in a hard-to-access sloping chimney section.
But installations to both 45° or 30° angles off from vertical (not from horizontal) are described by both standards and manufacturers.
If you going to proceed you should nevertheless review your installation plan with your local fire inspector.
To be clear, we are discussing a metal chimney installation, for an oil fired heating furnace, not a flue-vent connector or "stackpipe" - the term we use to describe the metal connector between the heating appliance and the actual chimney.
You would not run an uninsulated flue vent connector through an attic. A flue vent connector must slope at least 1/4" per foot of run. The heater manufacturer may have other specifications and limitations on flue vent connector length. We discuss flue vent connectors separately at FLUE VENT CONNECTORS, HEATING EQUIPMENT.
How about 30 degrees I read on another forum that was max
Reply: Example Manufacturers' Metal Chimney Slope, Length, Elbows, Angle Specification
A 30° metal chimney is when that angle is offset from vertical, closer to vertical than 45. Both can be acceptable provided you follow both the manufacturer's installation instructions and your local building code requirements. You'll see from an example we give below that depending on where you live there may be different constraints on permissible chimney slope, elbows, and non-vertical length.
You will also see that 15° offsets are described by various manufacturers.
Here is a typical insulated metal chimney installation guide from a manufacturer.
One pair of (two) 15° or 30° elbows may be used in an interior installation to provide an offset in order to avoid cutting of joists and
to clear other obstructions.
The maximum permissible angle with solid fuel installation is 30 degrees.
The vertical run of chimney above an offset must be supported with an elbow support.
Each elbow support will support 15 ft. (4.5 m) of chimney and the maximum length of chimney allowed between the elbows is 6' (2m).
Refer to the Offset Chart 1 on page 13 in these instructions for more details. Elbow kits contains 2 Elbows, 4 Locking Bands and an Elbow Support.
Here is a typical chimney or flue-vent connector slope (or pitch) guideline from a U.S. state code. There you will see that although the manufacturer may permit slopes of less than 45° a particular state guideline might not.
Pitch and length. Chimney or vent connectors shall have no more than two 45° offsets with the vertical. The horizontal length shall not exceed 75% of the total vertical height of the total venting system measured from the appliance outlet.
Chimney or vent connectors shall be pitched at least 1/4-inch per foot from the appliance outlet collar vent to the chimney inlet.
This category covers chimney and vent connectors and accessories which are engineered systems intended for connecting appliances to a vertical chimney or vent, or to reduce the clearances from connectors to combustible material in accordance with ANSI/NFPA 211, "Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances," and ANSI/NFPA 54, "National Fuel Gas Code," or applicable local building code requirements.
The type(s) of fuel-fired heating appliances (e.g., gas, liquid, solid fuel) with which these connectors and accessories have been investigated are indicated in the individual certifications. This information, together with other restrictions of use, such as mounting position, are also marked on the product and/or detailed in the manufacturer's installation instructions furnished with the product. - retrieved 2018/02/12, original source:
UL-DDCY.GuideInfo Chimney and Vent Connectors and Accessories - source: database.ul.com/
U.S. Chimney Codes & Standards Addressing Sloped or Angled Flues & Chimneys
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purpose of the sloped Colonial chimney
(Apr 20, 2012) George Miller said:
What was the purpose of the sloped Colonial chimney. I was told that it was sloped to prevent rain from putting out the fire. Is this true?
Colonial masons often brought a more central chimney straight up into the attic floor then built the chimney on an angle specifically to cause it to exit the roof at the roof's highest point - the ridge. The reasons for that decision were both cosmetic or aesthetic and possibly for improved fire safety and in some conditions improved draft too.
Rain falling into a chimney can cause ugly creosote runs and drips into the fireplace - an event addressed by a chimney cap, not by a sloped flue.
Question: insulate the clean out door?
(Nov 5, 2014) Nathhan Miller said:
I have a fireplace with a chimney that slopes about thirty degrees above the damper towards the outer wall of the chimney, leaving it very difficult to clean debris above the damper. This space is about four feet from my chimney flue. Now I have installed a ceanout door on the outside of the chimney, twelve by twelve. My gflue is eleven by eleven. I put fire brick on the wall where part of the flueliner was broken out. Now my question, do I need to insulate the clean out door somehow?
Chimney cleanout doors are not normally insulated - and I'd be worried lest someone try doing so, especially if they applied a combustible material.
But you do want to be sure the door closes tightly so as not to subvert the chimney draft.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: email@example.com
Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at firstname.lastname@example.org
Roger Hankeyis principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
"Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
"Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
"Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
"Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection_Repair.php. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
NFPA 211 - 3-4 - Clearance from Combustible Material
NFPA 54 - 7-1 - Venting of Equipment into chimneys
Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
American Gas Association - New Vent Sizing Tables
Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
National Chimney Sweep Guild - Yellow Pages of Suppliers
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones